Li-ion power mod

Re: Li-ion power mod

Postby aiyiadam » Thu Dec 27, 2018 4:46 pm

Lots of great ideas here. Maybe this could be simpler and faster solution for those like me, who aren't that skilled.

For DSO Shell I had bought a cheapish step-up USB cable (Unnlink brand) and was using it with a powerbank. Since the cable is too bulky and there is enough space in the DSO Shell, I have decided to put the circuit board in the device. Soldered a mini USB connector and a 100uF capacitor for getting rid of some ripple (As advised somewhere in this forum). And for attaching the DSO Shell to the 5000mAh powerbank I have used some velcro.

Later I could make a shorter cable and build a stand for the powerbank, but probably those won't be necessary.
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Re: Li-ion power mod

Postby upsss » Thu Dec 27, 2018 7:02 pm

@aiyiadam, Good idea if you can live with an external power bank (everyone has one) and can install a small step up module inside the scope. Instead of using a 9V Step-Up USB cable, taking it apart and soldering a mini USB connector, all you need is this $0.75 module https://www.ebay.com/itm/DC-DC-5V-9V-12v-28V-2A-Boost-Converter-Adjustable-Step-Up-Power-Supply-Module/183006469980?.
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Re: Li-ion power mod

Postby aiyiadam » Thu Dec 27, 2018 7:37 pm

@upsss Thanks for the tip. If I didn't have the step-up cable, I would definetly prefer to use a step-up module like that.
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Re: Li-ion power mod

Postby carlos » Mon Dec 31, 2018 7:31 pm

upsss wrote:It is unpredictable and it will vary from unit to unit. Basically at around 7.5V, which could actually be 7.5V ±0.5V the +5V and the -5V regulators will stop regulating and then anything is possible. The problem is that at that point the scope will NOT just die but will stop functioning properly and the results will be unpredictable.

Okay, thanks for the clarification! I'll make sure not to rely on any measurements made on low battery for the time being (lucky that I spend so much effort on the charge level indicator; though it turns out one with a number display would have been even better). If it's too bad, I can still add a step up (will probably have to lose one of the cells then).

upsss wrote:You can raise a little this minimum input voltage by about 0.6V by shorting out the D2 diode

I know, I did that :).

upsss wrote: Take a look at the bottom of the first page of this thread, you will see my implementation of this project. BTW, I am a EE so I know what I am talking about.

I'm not doubting you, and I saw your post, beautiful work! I just somehow had gotten it into my had to do it without a regulator, completely forgetting about the minimal input voltage of the regulators…
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Re: Li-ion power mod

Postby MorganFlint » Mon Jan 21, 2019 5:20 pm

upsss wrote:It is unpredictable and it will vary from unit to unit. Basically at around 7.5V, which could actually be 7.5V ±0.5V the +5V and the -5V regulators will stop regulating and then anything is possible. The problem is that at that point the scope will NOT just die but will stop functioning properly and the results will be unpredictable.

You can raise a little this minimum input voltage by about 0.6V by shorting out the D2 diode next to the power input connector. Other than that, I would strongly suggest using just one Lithium battery and using a step up converter with an output of 8.0-8.5V (still short out D2, there is no need for it). You will be able to fit a larger battery and get much longer run time. Take a look at the bottom of the first page of this thread, you will see my implementation of this project. BTW, I am a EE so I know what I am talking about.

Hello, upss, I tend to agree with all your comments about the problems of feeding regulators with voltages too close to the intended output in both cases (when it was suggested with one cell to feed the digital board and with two cells for both analog & digital). As you said, this can lead to unpredictable behavior and incorrect readings.

However, in the design of the relatively new DSO138 mini (analog and digital board schematics), curiously, Jyetech has adopted the alternative of feeding all directly from a single cell (in battery mode; with USB connected it feeds from its 5V).

I'm not sure if this approach is very "orthodox"; at least, it won't be possible to use the battery to its full capacity, as the digital part has a 3.3V linear regulator this would limit minimum battery voltage to about 3.4V. Also, as the op amps AV+ and AV- are directly taken from the battery (the latter converted to negative with an ICL7660), the performance of the analog chain would be dependant on the battery charge. Something like this also happened in the early versions of DSO150, and motivated the mods proposed on this thread and on this article of Elektor magazine, where the +-5V regulators were included, as they were in the later versions of DSO150 analog boards to avoid, among other issues, the variation of the zero level line when changing sensibility.

What do you think?
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Re: Li-ion power mod

Postby upsss » Tue Jan 22, 2019 5:21 am

@MorganFlint, eliminating the ±5V regulators and powering everything from 5V is probably OK. However, powering it directly from a single lithium cell it is a bad idea. That kit doesn't have a battery charger circuit and no low battery voltage indicator. The battery voltage could be all over the place and the 3.3V regulator may drop out of regulation without any warning. The 3.3V regulator BL8060-3.3 wort case condition, +2% tolerance + 210mV minimum dropout voltage the regulator will drop out of regulation at battery voltage of <3.6V (plenty capacity still left) and again, you can expect unpredictable performance of the scope!
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Re: Li-ion power mod

Postby MorganFlint » Thu Jan 24, 2019 9:25 pm

upsss wrote:...That kit doesn't have a battery charger circuit...

In fact, it's prepared for battery operation (see 2nd "improvement" listed here and this picture), although you need to add the JYE118 module (which includes the charger) as shown in the lower left part of the schematic. My previous post assumed this part of the circuit was implemented.

Anyway, as you say, it will only work OK until the battery reaches ~3.6V-3.4V (depending on the 3.3V regulator), with the added problem that it doesn't have a low battery voltage indicator (unless it's implemented in the firmware, but I doubt it as I don't see battery voltage routed to an ADC input).
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Re: Li-ion power mod

Postby upsss » Sat Jan 26, 2019 4:44 pm

I wouldn't use their JYE118, it doesn't solve any of their problems. If anything, I would use a USB 18650 power bank which has a built in charger and a step up converter to 5V. You can find these power banks with a battery cheaper than their JYE118. This way you have a constant 5V output, a built in USB charger with battery protection, low battery shut down and a large battery capacity.
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Re: Li-ion power mod

Postby MorganFlint » Tue Jun 04, 2019 4:05 pm

Although this thread is almost dead, for the sake of completeness, in this thread you can find the instructions about how DSO138mini implements battery power.
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Re: Li-ion power mod

Postby Leonardolb » Thu Sep 12, 2019 8:59 pm

Here's my mod.

I used:
1x MT3608 DC-DC Step Up Converter Booster Power Module
1x TP 4056 Micro USB 1A Lithium Battery Charger With Protection Module
1x (7 years old) Nokia Cellphone Li-ion Battery, 3,7V 1020 mAh

I do noticed some noise, but since we don't have other simple option (which won't involve main PCB rework), I think I can live with that :lol:
I tested the system and it worked for 3 hours until the battery reach the minimun safe voltage, but the board always received continuously 9V, only jumping the noise from 6kHz to almost 10kHz at the end.

Running Open DSO Shell 3.1 firmware.

And yes, I know that my device is a counterfeit one, tryied to argue with my local supplier but had no success, so I have to deal with what I have :oops:

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Testing

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Mounting

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Built

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USB Charging Port

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Charging (note the red light through the hole)
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